
der Hörer
receiver
The part of a traditional telephone that you pick up, hold to your ear, and speak into.
Als das Telefon klingelte, nahm sie sofort den Hörer ab.
When the phone rang, she immediately picked up the receiver.
receiver / listener
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receiver
The part of a traditional telephone that you pick up, hold to your ear, and speak into.
Als das Telefon klingelte, nahm sie sofort den Hörer ab.
When the phone rang, she immediately picked up the receiver.

listener
A person who listens to a radio program, a podcast, or a musical performance; a listener.
Der Radiosender bat seine Hörer, für ihren Lieblingssong abzustimmen.
The radio station asked its listeners to vote for their favorite song.

auditor
A person who attends lectures at a university or college without being officially enrolled in a degree program (guest auditor).
Als Hörer darf er an den Vorlesungen teilnehmen, aber keine Prüfungen ablegen.
As an auditor, he may attend the lectures but not take any exams.
The word 'Hörer' derives directly from the verb 'hören' (to hear/listen). The suffix '-er' forms a noun here that refers either to the person who listens or to the device used for hearing.
Wer war der erste Hörer, der die richtige Antwort wusste?
Who was the first listener who knew the correct answer?
The context makes it clear which meaning is intended. Words like 'Telefon' (telephone) or 'auflegen' (to hang up) point to the telephone receiver. 'Radio' or 'Podcast' point to the listener, and 'Universität' (university) or 'Vorlesung' (lecture) point to the auditor.
Er legte wütend den Hörer auf.
He angrily hung up the receiver.
In connection with the telephone, the most important verbs are 'den Hörer abnehmen' (to pick up the receiver; to start a call) and 'den Hörer auflegen' (to hang up the receiver; to end a call).
Als es klingelte, hat niemand den Hörer abgenommen.
When it rang, no one picked up the receiver.
In radio shows or podcasts, the direct address 'Liebe Hörerinnen und Hörer' (dear listeners) is a very common and classic greeting.
„Liebe Hörerinnen und Hörer, willkommen zu unserer heutigen Sendung!“
'Dear listeners, welcome to today's program!'
listener
Both words refer to a person who listens to something. „Hörer“ is particularly suitable for radio, podcasts, or a media audience in general. „Zuhörer“ places more emphasis on listening consciously and attentively, especially to a person who is speaking or performing.

Die Hörer konnten im Podcast eine neue Folge über gesunde Ernährung anhören.
The listeners could hear a new podcast episode about healthy eating.
Die Zuhörer folgten dem Vortrag aufmerksam und stellten danach viele Fragen.
The listeners followed the lecture attentively and then asked many questions.